Suction pipe for the removal of waste material in leather skiving machines equipped with rotating bell knife



May 31, 1960 BR UN 2 D. A 1 SUCTION PIPE FOR THE REMOVAL OF WASTEMATERIAL IN LEATHER SKIVING MACHINES EQUIPPED WITH ROTATING BELL KNIFEFiled Aug. 19. 1958 United States Patent SUCTION PIPE FOR THE REMOVAL OFWASTE MATERIAL IN LEATHER SKIVTNG MACHINES EQUIPPED WITH ROTATING BELLKNIFE Dieter Braun, Stuttgart, Germany, assignor to Fortuna WerkeSpezialmasehinenfabrik A.-G., Stuttgart-Bad Cannstatt, Germany FiledAug. 19, 1958, Ser. No. 756,921 4 Claims. (Cl. 69-95) The inventionrelates to leather skiving machines, and more particularly to theremoval of scrap therefrom.

Leather skiving machines with bell knives are essentially composed of arotating bell-shaped knife, which is continuously sharpened duringoperation by a rotating grinding wheel, a presser foot with a highlypolished guide face, and a feed roll with rough surface which extendsalmost half its diameter into the interior of the bell knife and bearswith its curved surface against the knife edge of the bell knife, fromwhich position it is permitted to yield downward against the pressure ofa spring. The purpose of the feed roll is two-fold: in the first place,to advance the material by means of its rough surface from under thepresser foot towards the cutting edge of the bell knife and, in thesecond place, to remove the burr which is likely to appear duringgrinding from the inner face of the knife edge. For this purpose, thefeed roll is spring pressed towards the bell knife and brought into theabove mentioned position of contact.

The scrap produced in skiving leather and other soft material can varyfrom strips of mm. minimum in thickness and less and of a fewmillimeters in width, up to strips of 2 to 3 mm. in thickness and a fewcentimeters in width, sometimes also up to several meters in length, alldepending on the kind of material and the skiving method used.

These thin strips of scrap material may cause serious disturbances inthe flow of work, if, because of their clinginess and the fibrousstructure of their surface, they adhere to the rough surface of thefeedroll and, on further rotation of the feed roll, get under the materialto be skived. If the material is to be skived to extreme thinness, anysuch scrap slipping under the work when the latter is being fed underthe presser foot, may cause the work to be damaged at this spot and tobe useless, while thicker material, if it deviates from the properdirection of feed, may indirectly disturb the work flow by blocking thefeed of material to the knife.

Efforts have been made to eliminate these difliculties by means ofscraping devices which are in close contact with the feed roll surface;however, satisfactory results could not be obtained in this way,especially because of the roughness of the feed roll.

Compressed air jets have also been used in place of mechanical scrapersfor the removal of scrap adhering to the feed roll, with the directionof the air jet opposite to the direction of rotation of the feed roll;though the waste material is then removed from the feed roll, it isnevertheless not cleared from the zone of danger around the bell knife.

Attempts have also been made to remove the waste material by suction.Suction devices directly connected to the scrap ejection hole require avery high blowing efliciency and thus are not economical. In addition,they cannot ensure that thin strips of waste material do not windthemselves round the feed roll. Even if the end of the suction pipe isadvanced into close proximity to the feed roll, so as to project partlyinto the hollow space 2,938,369 Patented May 31, 1960 ICC within thebell knife, these sucking devices, while removing eifectively any wastecollected within the bell knife, do not peel off the strips adhering tothe feed roll. Therefore, in order to remove such strips from the feedroll and out of the zone around the bell knife or feed roll, acompressed air jet generated by a compressor, and an additional suctionblower become necessary.

The primary object of the present invention is to provide a scrapremoval device which avoids the disadvantages of the prior art.

Another object of the invention is to provide such a device which iseconomical yet at the same time effective in removing the scrap.

A further object of the invention is to provide an arrangement in whicha single suction fan serves both to withdraw the scraps from theinterior of the bell knife and to remove scraps which otherwise mightstick to the feed roll.

This is accomplished in general by closing off to the outside air, bythe suction nozzle, the greater part of the area of the open mouth ofthe bell knife except for the portion adjacent the feed roll, therebyclosing off the intake of outside air to this area and creating aninflow of air in the area adjacent the feed roll which impinges on theroll as a jet directed against the inner surface of the roll (that is,the surface furthest from the knife edge) in a direction opposite thedirection of rotation of such surface so as to prevent scraps fromsticking to the feed roll and being carried by it around and under thework.

Specifically, with a conventional suction blower driven by the skivingmachine motor, and a suction pipe with a specially formed mouthpieceextending to the very area where waste material is produced, all kindsof scrap may be removed in the usual way by the provision of a wasteseparator or through natural gravity. The special shape of themouthpiece generates a sucking air current, which enters the hollowspace within the bell knife as an air jet of a direction which isopposed to the rotary direction of the strips adhering to the feed roll,thus preventing them from winding themselves around the feed roll. Allscrap will be removed from the feed roll by the blowing force of thesucked-in air current, and pulled into the suction pipe.

The mouthpiece covers at least half of the circular area of the hollowmouthof the bell knife, approaching the outer cylindrical wall of thebell knifeso closely that only a narrow slit is left between the knifewall and the suction pipe. Through this narrow slit air will also besucked in into the hollow space within the bell knife, thus preventingsmall dust-like scrap particles from escaping into the open air throughthis slit. In the zone of the feed roll the mouthpiece is given such ashape that its outside wall nearest the feed roll, in conjunction withthe feed roll, forms a funnel or nozzle-like aperture through which astream of air is sucked in into the interior of the bell knife. This hasthe jet impinge on the feed roll and has the effect of pulling olf anyscrap ma terial which tends to adhere to the feed roll. This jet,although directed at a sharp tangential angle towards the feed roll, isopposed in direction to the direction of rotation of said feed roll, sothat any scrap will be carried along by this stream of air through thesuction pipe, and be collected in a waste receptacle.

Those parts of the circular area of the bell knife not covered either bythe mouthpiece or by the feed roll, will nevertheless be filled out byparts of the bearing system and the drive parts for the feed roll. Theeffect of the eddies of air generated by these parts and by the freeedge of the bell knife is such that the volume of air passing this eddyzone will actually be smaller than would be expected, considering theratio of the corresponding cross-sectional areas.

There will scarcely be any eddies in the nozzle-like portion of the airentrance so that the volume ofv air passing this zone will be relativelylarge and will have a higher velocity because of the shape of thisnozzle. The higher air velocity due to this nozzleeifect will producethe necessary sharp stream of air required for the removal of scrapmaterial from the feed roll.

Further advantages and objects of the invention will appear more fullyfrom the following description, especially when taken in conjunctionwith the accompanying drawings which form a part thereof.

In the drawings: h

Fig. 1 is a vertical cross-section through a bell knife with a feed rolland the mouthpiece of a suction pipe; and

Fig. 2 is a view of the bell knife looking towards the knife edge.

Bell knife 1 with scrap ejector 2 rotates on the end of shaft 8. Feedroll 3 with hearing 5 and articuated drive shaft 6 extends by almosthalf its diameter into hollow space 9 within the bell knife 1. Itrotates in the direction of arrow a. Material to be worked is fed intowards edge 10 of bell knife 1 by feed roll 3 from under presser foot4. Grinding wheel 7 regrinds knife edge 10 if required. Any burrproduced in the regrinding process will be removed by slight contact ofthe feed roll 3 with the knife edge, the curved surface of the formercorresponding with the circular shape of the knife edge, and thecasing-line of the knife running nearly at a tangent with the surface ofthe feed .roll.

Suction pipe 11 covers with its mouthpiece a large portion of thecircular area of knife edge 10, leaving only a limited sector open inthe zone of the feed roll to permit a stream of sucked-in air to enterthe hollow space within the bell knife. The scrap material will besucked in through aperture 12 into suction pipe 11, and will beseparated in the usual way. The mouthpiece joins closely the outercylindrical wall of the bell knife without touching it, so as to allow astream of air to enter also through this slit formed by the bell knifeand the mouthpiece and to penetrate into the interior of the bell knife.The outer wall of the mouthpiece nearest the feed roll is curvedtransversely substantially to match the shape of the periphery of thefeed roll and is curved inwardly to form a nozzle of converging form asshown in cross-section in Fig. 1, so that, in conjunction with the feedroll, it forms a nozzle-like aperture 13 for the stream of air(indicated by arrow b) penetrating into the hollow space within the bellknife. The outer wall of the mouthpiece leaves enough space in the zoneof the grinding wheel 7 for the operation of said grinding wheel.

While I have described herein one embodiment of my invention, I wish itto be understood that I do not intend to limit myself thereby exceptwithin the scope of the claims hereto or hereinafter appended.

I claim: p

'1. In a leather skiving machine having a bell-shaped knife with an openmouth mounted to rotate about an axis and a feed roller having abarrel-shaped surface mounted to rotate about an axis transverse to theaxis of rotation of the knife and extending substantially half itsradius into the knife and having its surface adjacent the cutting edgeof the knife, and means to rotate said roller, scrap removal meanscomprising means closing off to the intake of outside air the greaterpart of the open mouth of the bell knife other than the area adjacentthe feed roll, andmeans to exert a suction within the bell knife,whereby air entering under such suction impinges on that portion of theperiphery of the feed roll remote from the inner wall of the bell knifein a direction opposing the direction of rotation of such portion so asto remove scrap therefrom.

2'. In a leather skiving machine having a bell-shaped knife with an openmouth mounted to rotate about an axis and a feed roller having abarrel-shaped surface mounted torotate about an axis transverse to theaxis of rotation of the knife and extending substantially half itsradius into the knife and having its surface adjacent the cutting edgeof the knife, and means to rotate said roller, scrap removal meanscomprising a suction mouthpiece fitting closely the cutting edge of theknife and covering substantially the whole area of the open mouth otherthan the area adjacent the feed roller, the area adjacent the rollerbeing open, whereby air drawn into this last'area impinges on thatportion of the periphery of the feed roll remote from the inner wall ofthe bell knife in a direction opposing the direction of rotation of suchportion so as to remove scrap therefrom.

3. In a machine as claimed in claim 2, said suction mouthpiece having acurved outer surface adjacent the feed roll which converges towards thefeed roll to form a nozzle for the air impinging on the feed roll.

4. In a machine as claimed in claim 2, said suction mouthpiece beingslightly spaced from the bell knife at points other than those adjacentthe feed roll forming a narrow slit through which air is sucked to drawdust-like particles into the mouthpiece.

No references cited.

